API interaction scripts in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this curl command?

You run this command to get JSON data from a public API:

curl -s https://api.agify.io?name=michael | jq '.age'

What will be the output?

Bash Scripting

curl -s https://api.agify.io?name=michael | jq '.age'

A Returns an error because jq is not installed

B Returns the entire JSON response as a string

C Returns the predicted age as a number, e.g., 69

D Returns the name field from the JSON

💡 Hint

jq extracts specific fields from JSON output.

The command fetches JSON data about the name 'michael' and jq extracts the 'age' field, which is a number.

📝 Syntax

intermediate

Which curl command correctly sends JSON data via POST?

You want to send JSON data '{"name":"Alice"}' to an API endpoint using curl. Which command is correct?

A curl -X POST -d '{"name":"Alice"}' https://example.com/api

B curl -X POST -H 'Content-Type: application/json' -d '{"name":"Alice"}' https://example.com/api

C curl -X POST -H 'Content-Type: text/plain' -d '{"name":"Alice"}' https://example.com/api

D curl -X GET -H 'Content-Type: application/json' -d '{"name":"Alice"}' https://example.com/api

💡 Hint

APIs expect the Content-Type header to match the data format.

To send JSON data, you must set the Content-Type header to application/json and use POST method.

🔧 Debug

advanced

Why does this bash script fail to parse JSON correctly?

This script tries to get the 'token' field from an API response:

response=$(curl -s https://example.com/api/login)
token=$(echo "$response" | jq '.token')

But token is empty. Why?

Bash Scripting

response=$(curl -s https://example.com/api/login)
token=$(echo "$response" | jq '.token')

A Because curl needs -X POST to get a token

B Because jq cannot parse JSON from curl output

C Because the API does not return a token field

D Because $response is not quoted, so echo splits it and jq gets invalid input

💡 Hint

Think about how bash handles variables with spaces or newlines.

Without quotes, $response loses its JSON structure when passed to echo, causing jq to fail.

🚀 Application

advanced

How to extract all user IDs from a paginated API using bash?

An API returns user data in pages. Each page has a 'users' array and a 'next_page' URL or null if last page.

Write a bash approach to collect all user IDs from all pages.

A Use a loop that fetches each page URL, extracts user IDs, appends them, and follows 'next_page' until null

B Fetch only the first page and extract user IDs, ignoring pagination

C Use curl with -L to follow redirects and get all pages automatically

D Use jq to merge all pages by calling the API once with a large limit parameter

💡 Hint

Pagination requires multiple requests following the next page links.

You must loop through pages, extract IDs, and continue until no next page is given.

🧠 Conceptual

expert

What is the main risk of using curl with user input in a bash script?

You write a bash script that takes a URL from user input and runs:

curl "$user_url"

What is the biggest security risk here?

A User input could contain malicious commands causing command injection

B curl might download large files and fill disk space

C curl might fail if the URL is malformed

D User input might cause curl to connect to unsafe servers

💡 Hint

Think about how bash interprets variables and special characters.

If user input is not sanitized, it can inject commands or options that run unintended code.

Practice

1. What is the primary tool used in bash scripts to interact with web APIs?

easy

A. sed

B. grep

C. awk

D. curl

Solution

1. Step 1: Understand the purpose of each tool

   curl is used to send HTTP requests, while grep, awk, and sed are text processing tools.

2. Step 2: Identify the tool for API interaction

   Since APIs communicate over HTTP, curl is the correct tool to send requests and receive responses.

3. Final Answer:

   curl -> Option D

4. Quick Check:

   API calls use curl [OK]

Hint: Remember: curl sends web requests in bash [OK]

Common Mistakes:

• Confusing text tools like grep with API tools
• Using sed or awk for HTTP requests
• Thinking bash has a built-in HTTP client

2. Which of the following is the correct syntax to send a GET request to https://api.example.com/data using curl?

easy

A. curl https://api.example.com/data

B. curl --data https://api.example.com/data

C. curl -d https://api.example.com/data

D. curl -X POST https://api.example.com/data

Solution

1. Step 1: Understand default curl behavior

   By default, curl sends a GET request if no method is specified.

2. Step 2: Analyze options

   curl https://api.example.com/data sends a GET request simply by specifying the URL. The other options either specify POST or data, which changes the method.

3. Final Answer:

   curl https://api.example.com/data -> Option A

4. Quick Check:

   Default curl = GET request [OK]

Hint: No method means GET by default in curl [OK]

Common Mistakes:

• Using -X POST when GET is needed
• Adding -d or --data without POST method
• Confusing GET and POST syntax

3. What will be the output of this script snippet?

response=$(curl -s -H "Accept: application/json" https://api.example.com/status)
echo "$response"

medium

A. An error message about missing POST data

B. The raw JSON response from the API

C. Nothing, because the script has a syntax error

D. The HTTP status code only

Solution

1. Step 1: Understand the command

   The curl command uses -s for silent mode and sets the header to accept JSON. It fetches data from the API URL.

2. Step 2: Analyze the output

   The response variable stores the full API response body, which is expected to be JSON. The echo prints this JSON string.

3. Final Answer:

   The raw JSON response from the API -> Option B

4. Quick Check:

   Silent curl with JSON header returns JSON [OK]

Hint: Silent curl (-s) returns response body only [OK]

Common Mistakes:

• Expecting HTTP status code instead of body
• Thinking -H sets request method
• Assuming syntax error due to quotes

4. Identify the error in this script that sends JSON data to an API:

curl -X POST https://api.example.com/update -d '{"name":"John"}' -H 'Content-Type: application/json'

medium

A. The JSON data is not properly escaped

B. The -X POST option is missing

C. The Content-Type header should be text/plain

D. The URL is missing the protocol

Solution

1. Step 1: Check JSON data quoting

   The JSON string uses double quotes inside single quotes, but the inner double quotes are escaped with backslashes, which is unnecessary and can cause errors in bash.

2. Step 2: Correct quoting for JSON in bash

   Use single quotes around JSON without escaping double quotes, or use double quotes outside and escape inner quotes properly.

3. Final Answer:

   The JSON data is not properly escaped -> Option A

4. Quick Check:

   Proper JSON quoting avoids escape errors [OK]

Hint: Use single quotes around JSON to avoid escaping double quotes [OK]

Common Mistakes:

• Over-escaping quotes inside JSON
• Wrong Content-Type header
• Omitting -X POST when sending data

5. You want to write a bash script that sends a POST request with JSON data and saves the HTTP status code to a variable. Which command correctly does this?

hard

A. status=$(curl -X POST https://api.example.com/api -d '{"key":"value"}' -H 'Content-Type: application/json')

B. status=$(curl -X POST -H 'Content-Type: application/json' https://api.example.com/api -d '{"key":"value"}')

C. status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s)

D. status=$(curl -X POST -d '{"key":"value"}' https://api.example.com/api -H 'Content-Type: application/json' -i)

Solution

1. Step 1: Understand how to capture HTTP status code

   The -w "%{http_code}" option tells curl to output the HTTP status code after the response. The -o /dev/null discards the response body, and -s silences progress.

2. Step 2: Check command correctness

   status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s) correctly uses all these options and assigns the status code to the variable. Other options either capture the response body or include headers, not just the status code.

3. Final Answer:

   status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s) -> Option C

4. Quick Check:

   Use -w with -o /dev/null to get status code [OK]

Hint: Use curl -w with -o /dev/null to get only status code [OK]

Common Mistakes:

• Capturing full response instead of status code
• Missing -w option for status code
• Not silencing output with -s